The minimization of electronics makes heat dissipation of related devices an increasing challenge. When the size of materials is smaller than the phonon mean free paths, phonons transport without internal scattering and laws of diffusive thermal conduction need to be revisited. This work reports the temperature dependent thermal conductivity of doped epitaxial 6H–SiC and monocrystalline porous 6H–SiC below room temperature probed by time-domain thermoreflectance. Strong quasi-ballistic thermal transport was observed in these samples, especially at low temperatures. Doping and structural boundaries were applied to tune the quasi-ballistic thermal transport since dopants selectively scatter high-frequency phonons while boundaries scatter phonons with long mean free paths. Exceptionally strong phonon scattering by boron dopants are observed, compared to nitrogen dopants. Furthermore, orders of magnitude reduction in the measured thermal conductivity was observed at low temperatures for the porous 6H–SiC compared to the epitaxial 6H–SiC. Finally, first principles calculations and a simple Callaway model are built to understand the measured thermal conductivities. Our work sheds light on the fundamental understanding of thermal conduction in technologically-important wide bandgap semiconductors such as 6H–SiC and will impact applications such as thermal management of 6H–SiC-related electronics and devices.

电子设备的最小化使得相关设备的散热成为越来越大的挑战。当材料的尺寸小于声子平均自由程时，需要重新审视没有内部散射的声子传输和扩散热传导定律。这项工作报告了掺杂外延 6H-SiC 和单晶多孔 6H-SiC 在室温以下通过时域热反射探测的温度相关热导率。在这些样品中观察到强烈的准弹道热传输，尤其是在低温下。应用掺杂和结构边界来调整准弹道热传输，因为掺杂剂选择性地散射高频声子，而边界散射具有长平均自由程的声子。观察到由硼掺杂剂引起的异常强烈的声子散射，与氮掺杂剂相比。此外，与外延 6H-SiC 相比，在低温下观察到多孔 6H-SiC 的热导率降低了几个数量级。最后，建立第一性原理计算和简单的 Callaway 模型以了解测量的热导率。我们的工作阐明了对技术重要的宽带隙半导体（如 6H-SiC）中热传导的基本理解，并将影响应用，例如 6H-SiC 相关电子设备和设备的热管理。建立第一性原理计算和简单的卡拉威模型以了解测量的热导率。我们的工作阐明了对技术重要的宽带隙半导体（例如 6H-SiC）中热传导的基本理解，并将影响应用，例如 6H-SiC 相关电子设备和设备的热管理。建立第一性原理计算和简单的卡拉威模型以了解测量的热导率。我们的工作阐明了对技术重要的宽带隙半导体（例如 6H-SiC）中热传导的基本理解，并将影响应用，例如 6H-SiC 相关电子设备和设备的热管理。